If all you need to do is to link to your LO from another website you don't really need to install Moodle to do that unless you want to control access via Moodle.
You can simply export an LO as a deployment zip, upload and extract somewhere online then link to the index.htm file. e.g. if you have cpanel access to your webserver as described just use the file manager to create a folder, upload and extract the deployment zip.
But you should be able to install XOT. Did you check the exact username, database name and permissions I mentioned previously? In cpanel select MySQL databases...
Current databases shows a list of Databases, Size, Privielged Users and actions. That should display the exact values you need to use for databasename and databaseusername which as I mentioned are usually accountname_databasename and accountname_databaseusername
If you do not see a database_username alongside your xerte database you need to select the option lower down to Add User to Database and select all privileges when doing so.
Then re-run the XOT /setup in your browser and follow the instructions.
HTH
Ron